This invention relates to a method of preparing trifluoroacetic acid, or trifluoroacetyl chloride if desired, from 1,1,1-trichloro-2,2,2-trifluoroethane.
Trifluoroacetic acid is useful as an intermediate material for some medicines and agricultural chemicals. For industrial preparation of this compound, 1,1,1-trichloro-2,2,2-trifluoroethane is one of the hitherto chosen starting compounds.
It is well known that trifluoroacetic acid is formed by the reaction of 1,1,1-trichloro-2,2,2-trifluoroethane with fuming sulfuric acid or anhydrous sulfuric acid in the presence of a suitable catalyst such as mercury sulfate, boron trifluoride (West German patent specification No. 2,947,376) or bromine (U.S. Pat. No. 4,340,548). However, disadvantages of this method reside in that the reactant acid is inconvenient for handling and that the post-reaction treatment of the waste acid is troublesome.
Also it is known that trifluoroacetic acid can be formed by a photochemical reaction of 1,1,1-trichloro-2,2,2-trifluoroethane in the presence of chlorine and water (J. Chem. Soc., 1959, 387). However, this method is not favorable for industrial practice because the reaction gives a small amount of hydrofluoric acid, which causes devitrification of glass used in the light source part of the reaction apparatus in a relatively short period of time, and also because the selectivity of the reaction to trifluoroacetic acid is not satisfactorily high.